Studies of miners exposed to radon have consistently shown that the miners are at increased risk of lung cancer death, and that the risk increases with dose of radiation. Extrapolating from data on miners, it has been predicted that residential exposure to radon may lead to a significant number of lung cancer deaths in the U.S. There is still uncertainty, however, about the extent to which concomitant exposures in the mines modify the risk of lung cancer. Furthermore, these same studies of miners have suggested small but inconsistent radon-related risks for other cancers, but no study has been large enough to convincingly demonstrate such effects. The focus on mortality rather than cancer incidence may have made it difficult to detect risks for cancers with good survival. We will conduct a cancer incidence follow-up study and a series of nested case-cohort studies of specific cancers in a population of approximately 18,000 underground uranium miners who started working in the Pribram uranium mining region in the Czech Republic between 1948 and 1976. This represents one of the largest cohorts of uranium miners studied. The main objectives are to establish 1) whether the risk of specific cancer sites, sub-sites, and histologic types is higher in the miners than in the general population; 2) whether the risk of specific cancers increases with increasing dose of alpha-radiation; and 3) whether the relationship between lung cancer and radon exposure is modified by other risk factors, such as smoking, dust and arsenic.